Experience with GCLs used as a conductive layer in geomembrane leak-location surveys
Engineers, installers, regulators, and owners are starting to rely on geomembrane leak-location surveys as part of the construction quality assurance for landfills. The various methods are described in ASTM Standard D 6747.' Standard procedures for conducting leak-location surveys of geomembranes covered with earth materials are described in ASTM Standard D 7007.2
Figure 1 shows the principle of the method. The electrical method is to detect the points where electrical current flows through holes in the geomembrane and requires electrically conductive media above and below the geomembrane being tested. For leak-location surveys of landfill geomembranes covered with earth materials, the earth materials provide the conductive layer above the geomembrane.
Often a geosynthetic clay liner (GCL) is used under the primary geomembrane This GCL has been used as the conductive layer under the geomembrane on many successful geomembrane leak location surveys for more than 10 years.
Design and preparation factors
In some cases, a successful geomembrane leak-location survey depends not only on the proper performance of the survey itself, but also on the design of the liner system and proper preparation of the liner system prior to testing. Smith et al/ describe in detail those factors that will influence the performance and sensitivity of a geomembrane leak-location survey The technical paper provides excellent guidance and should be consulted during the design of geomembrane liner systems if a leak-location survey is specified or evenly remotely possible.
Although major construction damage can usually be found, certain landfill liner designs can reduce leak detection sensitivity and hinder the detection of holes. In single-geomembrane designs, or in double-geomembrane designs with a clay or drainage layer between the geomembranes. the earth materials readily provide the required conduction layer under the primary geomembrane.
In some applications, instead of using a thick earth material layer between the geomembranes, a GCL is installed. Most GCLs consist of a thin layer of sodium bentonite sandwiched between two geotextiles. Sometimes the bentonite/adhesive layer is laminated to a geomembrane.
GCLs are used in place of a thick compacted clay liner where clay is not available or is expensive GCLs provide an equivalent low permeability layer with the advantages of being very easy to install, not requiring a nearby clay source, not taking up air space, and not being subject to construction delays that may be needed to dry or wet the clay to allow proper clay compaction.